This invention relates generally to a gear pump and, more particularly, to a gear pump which is especially adapted to supply pressurized liquid fuel to an oil burner. Gear pumps of this general type are disclosed in Harwath U.S. Pat. Nos. 4,171,939; 4,685,871; 4,728,271; and 4,958,997 and in Hunsberger et al U.S. Pat. No. 4,391,580.
In pumps of this type, it is conventional for a spur gear to be secured to the free end portion of a rotatable drive shaft having a free end which normally is disposed in spaced opposing relation with an end plate. The shaft is supported for rotation by the pump body and the gear is located between the body and the end plate. Conventionally, the gear is secured to the shaft with a tight press fit but also is coupled to the shaft by a key which transmits torque between the shaft and the gear in the event excessive torque and wear reduce or eliminate the torque-transmitting capability of the press fit.
In the pump disclosed in the Harvath '939 patent, the key is in the form of a cylindrical pin which fits into a slot in the shaft and into keyways in the bore of the gear. The arrangement of the pin, the slot and the keyways causes the gear to engage the end plate if excessive endwise thrust is exerted on the shaft during handling or during operation and prevents the end of the shaft from impacting against and being damaged by the end plate. In the Harwath '939 arrangement, however, the shaft is capable of being pulled out of the gear in a reverse direction by an axial force sufficient to overcome the press fit between the shaft and the gear.
The shaft of the pump disclosed in the Harwath '871 patent cannot be pulled reversely out of the gear by an axial force. This is achieved by hot upsetting the end of the shaft so that the key becomes trapped between the hot upset and the axially facing ends of the keyways if a pulling force is exerted on the shaft. In this pump, however, the shaft is capable of moving toward and impacting against the end plate. Because the shaft is relatively small in diameter, the end plate area for resisting the impact also is relatively small and thus damage can result and cause the pump to lock up or otherwise fail.